1. Field of the Invention
The present invention relates to an exposure apparatus, and more particularly, an exposure apparatus for a flat panel display (FPD) device and a method of exposing using the exposure apparatus.
2. Discussion of the Related Art
As the information age progresses, flat panel display (FPD) devices having light weight, thin profile, and low power consumption characteristics are being developed and are commonly substituted for cathode ray tube (CRT) devices. Generally, display devices may be classified according to their ability for self-emission as either emissive display devices or non-emissive display devices. Emissive display devices display images by taking advantage of their ability to self-emit light, while non-emissive display devices require a light source since they do not themselves emit light. For example, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices are commonly used emissive display devices. Liquid crystal display (LCD) devices may be categorized as non-emissive display devices and are commonly used in notebook and desktop computers because of their high resolution, capability of displaying colored images, and high quality image display.
One type of LCD device is the active matrix type LCD device in which a plurality of pixels are arranged in a matrix, and switching devices such as an independently controllable thin film transistor (TFT) are provided for each pixel in the matrix.
For example, one active matrix type LCD device utilized for a screen of a notebook, a television, a monitor or the like includes first and second substrates facing each other and a liquid crystal layer interposed therebetween. The first substrate or array substrate includes a plurality of gate lines and a plurality of data lines crossing each other to define a plurality of pixel regions. Further, a plurality of TFTs are disposed at the crossings of the plurality of gate lines and the plurality of data lines, wherein each of the plurality of TFTs corresponds to one of the plurality of pixel regions and is connected to each of a plurality of pixel electrodes formed in the respective one of the plurality of pixel regions.
In addition, the second substrate or color filter substrate includes: a black matrix overlapping with a non-pixel region of the first substrate such as a region occupied by a gate line, a data line, or a TFT; red, green and blue color filters repetitively arranged in an order in the plurality of pixel regions; and a common electrode disposed on the black matrix and the color filters.
The LCD panel is a non-emissive display device utilizing a light transmittance difference generated by an electric potential difference applied between the pixel electrode and the common electrode to generate images. Because a light source is required for viewing the generated images, LCD devices may further include a backlight unit. The LCD device can generate a multi color display by selectively combining red, green, and blue filtered light using a transmittance difference in each pixel and light emitted light from the backlight unit. The plurality of patterns such as the gate line, the data line, the pixel electrode and the common electrode, may be formed using a sequential process including depositing a thin film on a substrate; using a photolithographic process to form a photoresist layer for exposing a portion of the thin film; and employing an etching process to remove the exposed portion of the thin film.
An example photolithographic process includes coating a photoresist material on the substrate deposited the thin film; exposing a portion of the photoresist layer using a mask having a predetermined pattern; and developing for removal either the exposed portion or a non-exposed portion of the photoresist layer, thereby obtaining a photoresist pattern having the same shape as the predetermined pattern of the mask.
The demand for large-sized and high-resolution flat panel display devices have placed increased demands on the photolithographic process. In particular, the manufacture of large-sized and/or high-resolution devices requires that the exposing process be performed more accurately and precisely, and improvements in the exposure apparatus used in the exposing process are in high demand.
FIG. 1 is a schematic perspective view showing an exposure apparatus for a flat panel display device and a method of exposing according to the related art.
As shown in FIG. 1, an exposure apparatus 1 for a flat panel display device according to the related art includes a light source 10 for emitting ultraviolet rays or X-rays, a mask 20, and a stage 30 having a horizontal support surface 32 on which a substrate 2 is disposed. The mask 20 is horizontally arranged in correspondence with a surface of the stage 30. A thin film 4 is disposed on the substrate 2 and a photoresist layer 6 is disposed on the thin film 4. The mask 20 includes a transparent base substrate (not shown) of quartz and a pattern 24 made of an opaque material such as chromium (Cr) disposed on the transparent base substrate. Although not shown, a transmissive region and a shielded region are defined in the mask 20, and the pattern 24 is disposed in the shielded region. A portion of the transparent base substrate exposed by the pattern 24 is disposed in the transmissive region.
Hereinafter, an exposing process using the described related art exposure apparatus 1 will be explained.
The exposing process includes disposing the substrate 2 on the horizontal support surface 32 of the stage 30; horizontally arranging the mask 20 in correspondence with the substrate 2; and irradiating light from the light source onto the photoresist layer 6 on the substrate 2 through the mask 20 to transfer an image of the pattern 24 to the photoresist layer 6. Depending on the photosensitivity type of the photoresist layer 6, either the irradiated or the non-irradiated portion of the photoresist layer 6 is removed in a developing process. For example, when the photoresist layer 6 corresponds to a positive type, the irradiated portion of the photoresist layer 6 is removed during developing and the non-irradiated portion remains as a photoresist pattern (not shown). On the other hand, when the photoresist layer 6 corresponds to a negative type, the non-irradiated portion of the photoresist layer 6 is removed during developing leaving the irradiated portion of the photoresist layer 6 remaining as the photoresist pattern.
In the developing process, a developer is used to form the photoresist pattern. For example, when the photoresist layer 6 corresponds to a positive type in FIG. 1, the developer removes the irradiated portions of the photoresist layer 6, and the photoresist layer 6 is patterned into the photoresist pattern corresponding to the pattern 24 of the mask 20 exposing a portion of the thin film. The portion of the thin film (not shown) exposed by the photoresist pattern is removed in an etching process, thereby obtaining a desired thin film pattern.
The manufacture of a large-sized flat panel display device requires that the size of the mask 20 for the exposure apparatus 1 be correspondingly large-sized. However increasing the size of the mask 20 may create problems. First, when the mask 20 is large-sized, the weight of the mask 20 is correspondingly large. When a large sized mask 20 is horizontally arranged with respect to a surface of the substrate 2 in the exposing process, the center portion of the mask 20 may flex under its own weight in the direction of the force of gravity. The flexing of the mask 20 results in a distortion of the pattern transferred to the photoresist layer 6.
When using the exposure apparatus 1 of the related art the mask 20 is supported at its edges rather than at the center portion of the mask 20, which is in the main or transmissive region. Accordingly, flexing of large-sized masks results from the use of the related art exposure apparatus 1.
Further, the horizontal arrangement of the mask 20 facilitates the accumulation of unwanted particles on the surface of the mask 20. These particles may produce image defects. For example, a dot defect may occur when a particle present during the exposing process acts as an obstacle to transcribing a pattern to the photoresist.
This flexing phenomenon may be founded in the substrate having a size of about 1500·1850 mm and the mask having a size of about 1100·1300 mm for the substrate. The phenomenon may be aggravated as the sizes are increased.
FIG. 2 is a schematic cross sectional view taken along a line II-II of FIG. 1 illustrating flexure of a mask.
As shown in FIG. 2, the center of the mask 20 has a flexure portion at its center due to flexing of the mask 20 under its own weight and the surface of the mask 20 is covered with the particles 40.
Because the flexure of the mask 20 and the attachment of particles 40 to the mask 20 may be related to pattern distortion of the photoresist pattern and consequently the thin film pattern, it has been suggested that thickness of the mask 20 be increased and that the processing time be shortened. However, these suggestions lead to increased product cost.
Because the transparent base substrate of the mask 20 is selected from an expensive material such as quartz, increasing the thickness of the mask increases the product cost of the LCD device. Increasing the thickness of the mask also increases the weight of the mask, which may further contribute to flexure, so that the suggestion to increase the thickness of the mask may not effectively solve the identified problems. Further, additional problems may occur in the support unit supporting the mask 20 when the weight of the mask 20 increases.
Furthermore, as processing time is shortened, the probability of forming defects in the mask 20 increases. The time-shortened processes also have the disadvantage of being complicated and inefficient.